Anything that goes near the water sucks IMO, I have this:
http://www.sears.com/sr/javasr/produ...ers+%26+Cables
and just hook up when I get home if I feel the need, But I have gone all season never charging anything most of the time.
What I have and love is a battery Jump starter, I can run eletric reel all day, or a bait tank most of the day.
I never leave home with out it!